A new active state in CH Cygni, and a possible model

UBVIJHK photometry and spectroscopic observations of CH Cygni, an object with an irregular light curve, are discussed which reveal the onset of a new active state in March 1977. A provisional model of CH Cygni is outlined which involves mass transfer from a cool red giant to a hot dwarf via a transient accretion disk with a hot spot. It is shown that such mass exchange is feasible in the system and that the red giant need not fill its Roche lobe completely in order for mass outflow to commence. In terms of the proposed model, the evolutionary status of CH Cygni is interpreted as being close to that of a symbiotic star.